The present invention relates generally to connecting an end cap to a pressure cylinder, and more particularly to a pressure cylinder using a composite pressure barrel with tapered ends and a metal split tapered collar for interlocking a steel end cap to the composite barrel. The pressure cylinder of the present invention is particularly useful in pneumatic and hydraulic applications, or in general terms, fluid power distribution.
Typically, metal pressure cylinders can be constructed with threaded end caps or with the use of retaining tie-rods. Because steel has a high shear stress, these types of cylinders can be used at pressures up to and exceeding 10,000 psi. However, there are many drawbacks to using steel for pressure cylinders, including corrosion caused by contaminants carried in the fluid, excess weight, and high costs of fabrication and machining.
Although the tie-rod construction has become more common place, the threaded end cap design may still be found in lower pressure metal cylinder applications. The threaded end cap design has threads cut in the outer periphery of the steel barrel to accommodate mating with a threaded steel end cap to retain internal pressure.
The tie-rod design uses flat end caps and has multiple tie-rods extending the length of the fluid cylinder for bolting the end caps together about the outer periphery of the cylinder. The tie-rod design adds additional weight, excess costs, and provides a large and bulky pressure cylinder. A further disadvantage is that since the rods, washers, and nuts are typically all steel, excessive corrosion occurs to these assembly pieces when exposed in corrosive operating environments.
To overcome the disadvantages of using steel, some manufacturers have investigated the use of composite tubing for the barrel of the pressure cylinder. However, because composite materials typically have low shear stress properties, it is not practical to thread such composites and attempt to distribute the force of internal pressure through the threads to a threaded end cap. Any degree of high internal pressure will ultimately result in failure of the composite threads.
Alternatively, prior art attempts to use composite pressure cylinders have relied on the tie-rod design, and as previously discussed, the use of the tie-rod and flat cap design adds excess weight and costs to the pressure cylinder, as well as resulting in large and bulky pressure cylinders. Further, since the rods, washers, and nuts are typically all steel, corrosive operating environments cause excessive corrosion to these assembly pieces, resulting in added costs when repairing the pressure cylinders, and when disassembling for regular maintenance.
Therefore, it would be desirable to have a pressure cylinder and end cap assembly using a composite pressure barrel with minimal metallic assembly pieces that could withstand burst pressures exceeding 12,000 psi.